yeah koub you're right, every single feed belt needs to be full, but you can add a simple circuit to stop the belt in that case.

the circuit is that simple: one wire on each feed belt (read, hold) that goes into one arithmetic combinator (each + 0) then wire the output of this combinator to the very first belt of the sushi belt (enable/disable, [signal outputed by the combinator]>[4 times the number of belt minus 1])

and please do note that it is not needed for the triple item part (yellow, purple and white science packs) because they already are lacking a belt (splitters works in power of 2) and they are regulated with the yellow belts (one yellow belt being 1/3 of a blue one, it makes sure that the sushi belt will never get more than 1/3 of one of those belts)

I think the combinators are not needed.
The Sushi will stop beeing perfect if belts are not backing up - true.
But the belt will always "clean" itself and will add the missing items back into the loop as soon as they come back.

I think the combinators are not needed.
The Sushi will stop beeing perfect if belts are not backing up - true.
But the belt will always "clean" itself and will add the missing items back into the loop as soon as they come back.

No, it won't. It can't 'clean' itself because there's no mechanism that lets items leave the loop once it has been overfilled with any item. And once it is overfilled it will lock up. And when it locks up no item can enter. And no machines will pick up from the sushi belt if the items at their inserters are not the correct ingredient at that moment.

well the purpose of this isn't to be compact (we can't really talk about work since there are blueprints) but to be powerful and beautiful.
you're mainly right on the clogging part, any overfed item will stack between its scavenge filter splitter and its first splitter, but if these items are consumed until they complete the full loop it won't clog, that's why I said that it depends on the use case.

anyway feel free to not use my design, I don't claim it to be the best, I just simply love it :D

well the purpose of this isn't to be compact (we can't really talk about work since there are blueprints) but to be powerful and beautiful.
you're mainly right on the clogging part, any overfed item will stack between its scavenge filter splitter and its first splitter, but if these items are consumed until they complete the full loop it won't clog, that's why I said that it depends on the use case.

anyway feel free to not use my design, I don't claim it to be the best, I just simply love it

It's a neat experiment. And I do like it. I just think Dave's design is better for practical play since it allows you to not worry about the items that are looping back.

For your particular design, if you can guarantee that it doesn't clog up by having a factory eating everything from the sushi belt, then the loopback is completely pointless because it will always be empty. Anything looping back can clog your factory if it isn't at some point taken before it's too late. It won't stop clogging if you don't feed the belt back into the sushi mixer, but having can only be useful when you stop the input whenever anything is missing and if you make sure you start it up correctly again.

I'm doing my own sushi experiments. Sushi belts are cool even if they are usually a bit impractical. But there are methods to make sure they at least work reliably.

But here are some logical steps that lead to a conclusion.

The most important part of sushi belts (if used in a factory for "practical" use and not just as art) is that you want items to eventually reach the machines that use those items as ingredients.

For that to happen there needs to be space for everything needed to enter the sushi loop.

And that can only happen if the belt is always moving (or growing. But then it has to grow at the speed it moves. Forever).

And that can only happen if everything ends up in a machine or have space to loop back to the beginning again.

And it can only have space to re-enter if you don't fill it completely with a (strict) subset of the items you want on the belt (Factorio belts stop completely when 100% filled but the tiniest gap is enough to keep it moving) or make room by removing things that you have too much of.

And the items that are removed enter a reserved buffer space so they aren't in the way for the flow. This buffer space needs priority as input to back into the belt before the newly produced items that have never looped before or they might never get used and items will always constantly be produced and buffered indefinitely.

But the buffer needs an indefinite size anyways because you don't know in advance how long the items on the sushi belt will not be consumed. You have such a buffer, but it's 2 belts long (for each item on the 32 item sushi belt) so pretty far from infinite q:

Since removing items and placing them in infinite buffers is not that great I prefer never letting any belt be filled with more than its dedicated share of the belt.

Sorry for using stone. I don't have space science yet on my new map.
Take care when connecting the inputs - the sushi is lane sensitive...
And thanks xaetral for the idea on how to make this sushi.
This science build is visual more pleasing for me than using the filter inserter trick.

Please do note that:
1) the idea does NOT come from me, someone on discord posted this design it, I then designed my own version with cleaner belts
2) it is not fully functionnal, there are still a few bugs to deal with (the belts keep getting overfed and there are no combinator circuits yet)